1. Field of the Invention
The present invention relates to systems and methods for monitoring the concentration of a volatile, weakly soluble material dissolved in a liquid such as wastewater.
2. Description of the Related Art
Federal and state regulations impose standards for permissible levels of organic material in effluent streams. Regulations for the discharge of organic material, especially carbon tetrachloride (CCl.sub.4) and chloroform (CHCl.sub.3), are becoming increasingly stringent. In some cases, an upper limit for these materials is in the parts-per-billion range.
Thus, the need often arises for monitoring the concentration of weakly soluble, volatile materials in a liquid, such as wastewater. For example, manufacturing plants use water to scrub the by-products of their processes. This wastewater is then discharged as effluent into nearby streams and rivers. In a typical plant, the wastewater discharged contains some type of organic material. Also, it is often desirable to simply monitor the concentration of material dissolved in a liquid without altering the concentration of the material, such as in an environmental impact study.
Current practice is to analyze effluent periodically with a purge and trap sparging system which uses a gas chromatograph or other analytical instrument for monitoring the concentration of the material. In this system an inert gas is bubbled through a liquid which contains the dissolved material. The liquid is contained in a specially-designed purging chamber at ambient temperature. The material is transferred from the liquid phase to the gas phase. The gas from the gas phase is swept through a sorbent trap where the material is trapped. After purging is complete, the trap is heated and backflushed with the inert gas to desorb the material into an analytical instrument, such as a gas chromatograph, which monitors the concentration of the material. The gas chromatograph is temperature programmed to separate the material. The gas is then released from the system to the atmosphere.
This sparging system requires anywhere from 15 to 30 minutes for a reading of the concentration of the volatile material dissolved in the liquid. This analysis time allows only intermittent sampling, so that possible high-concentration excursions of the system may well be missed. Also, this system samples relatively small volumes of liquid (i.e., 20 ml. per sample), which is not a sufficient volume of liquid to average possibly heterogeneous samples. Consequently, this system cannot ensure high sensitivity of the concentration measurement.
The same type of analysis as described above for the purge and trap system has been performed on a more nearly continuous basis in another type of sparging system. However, this system requires more time between cycles of operation. This system also samples relatively small volumes of liquid, and thus, as in the above-described system, is not sufficient to ensure high sensitivity of the concentration measurement. Also, this system uses relatively small diameter piping (e.g., piping having a 1/16" outer diameter), which is subject to fouling from typical wastewater samples.
Therefore, it is an object of the present invention to provide a system which can monitor the concentration of volatile material dissolved in a liquid on a nearly continuous basis and which samples large volumes of liquid in such a way as to ensure high sensitivity of the concentration measurement.
It is also an object of the present invention to provide a system for monitoring the concentration of volatile material dissolved in a liquid which continuously re-uses the same supply of gas to enhance the transfer of material from the liquid phase to the gas phase, thereby ensuring full equilibration of the gas/liquid system for maximum sensitivity and determinability of concentration.